In the past, there have been many various types of magnet systems designed to provide a uniform magnetic field within a predetermined volume of space. One such type of magnet system is a magnetic resonance imaging (MRI) system which is typically used for spectroscopy on patients to detect abnormalities in living human cell tissue. Importantly, it must be possible to effectively position a patient in the uniform magnetic field. Accordingly, different types of MRI system designs have been used to establish a uniform field within a specified volume (e.g. a sphere) of sufficient size to allow a patient to be positioned in the field. To accomplish this, some earlier MRI systems have incorporated a pair of parallel magnetic pole plates to establish the field and have spaced the plates far enough apart to allow a patient to be positioned between them. In another configuration, other earlier MRI systems have incorporated a hollow cylindrical magnet system with magnetic coils surrounding the hollow interior of a cylinder into which the patient is placed. Both of these MRI system structures are "closed" in the sense that when a patient is positioned within the useful magnetic field, the patient is "closed" in. In other words, the structures are such that the patient's whole body must be positioned inside a structurally confined space, with magnet system components located above, below, and to the sides of the patient.
While such systems may provide a satisfactory uniform magnetic field, they do so with some disadvantages. For one thing, many patients develop claustrophobic reactions resulting from closed space structures. Another disadvantage is that during the time the patient is positioned inside such MRI systems, access to the patient is limited. There is little or no ability for physicians and others to perform other diagnostic procedures or operations on the patient while the patient undergoes magnetic resonance imaging.
Another disadvantage of conventional MRI systems is that they require support of the heavy magnets and components needed to generate magnetic field uniformities at the intensity required for useful spectroscopy. Structural support for magnet systems must be of sufficient size and strength to provide an adequate margin of safety for the patient, who may be positioned beneath heavy components. Unfortunately, extra precautionary design measures to ensure safety entail added material, manufacturing, and operating costs to MRI systems.
Accordingly, the present invention recognizes the need for a magnetic resonance imaging system which has a substantially open design that permits increased accessibility to the patient and eliminates heavy system components from being suspended above the patient. The present invention accomplishes this by providing a magnet system in which the magnetic field generating components are located substantially beneath the patient.
Accordingly, it is an object of the present invention to provide a substantially open design magnet system for generating a uniform magnetic field. Another object of the present invention is to provide a magnet system which allows a uniform magnetic field to be produced in a volume located substantially to one side of the magnetic field generating source. It is yet another object of the present invention to provide a magnet system which provides a uniform magnetic field sufficient for magnetic resonance imaging which allows easy access to patients during imaging. Still another object of the present invention is to provide a magnet system which accommodates patients without causing discomfort. Another object of the present invention is to provide a magnet system which is convenient and reliable in use, and cost-effective in manufacture.